Rotary hook construction for sewing machines



June 21, 1960 J. G. ATTWOOD 2,941,488

ROTARY HOOK CONSTRUCTION FOR SEWING MACHINES 2 Sheets-Sheet 1 Filed Aug. 6, 1957 FIG.I

June 21, 1960 J. G. ATTWOOD 2,941,488 ROTARY HOOK CONSTRUCTION FOR SEWING MACHINES Filed Aug. 6,1957

2 Sheets-Sheet 2 FIG.7

2,941,488 ROTARY HOOK CONSTRUCTION FOR suwnvc MACHINES John G. Attwood, Oak Park, 11]., assignor to Union Spehglsachine Company, Chicago, 111., a corporation of o Filed Aug. 6, 1957, Ser. No. 676,542

11 Claims. (Cl. 112.428

The present invention relates to'improvements in the construction of rotary hooks of the character used in lockstitch sewing machines. It has particular reference to hooks of this character which have a raceway in the -rotary component or hook body that is slightly eccentric to the axis of rotation of such component. The eccentricity of the raceway which cooperates with a projecting rib on the stationary bobbin case holder serves automatically to provide a gap between the shoulder on such holder and that on a finger which prevents rotation of the bobbin case holder by the frictional drag of the rotating hook body. It has heretofore been found that by offsetting the center of the raceway in relation to the axis of the shaft which carries the hook body, i'n'tlife proper direction relative to the loop seizing beak of the hook, the specified gap may be provided at the desired time to permit the passage therethrough of a branch of the needle thread loop. This has eliminated the necessity of special hook opening devices.

It has been found that hooks of the character indicated, as heretofore constructed, have not been capable of operation at speeds above about 10,000 r.p.m. This has placed a top speed of between 5000 and 5200,

rpm. for the machine itself. Such limitation has been imposed by the tendency of the rib and raceway of, a conventional hook to seize or weld or gall when the hook is operated at higher speeds. sive heating and wear of one or both of the cooperating surfaces, particularly in the region of maximum eccentricity of the raceway, i.e. in the region of the raceway adjacent the radial line extending from the axis of the atom R 2,941,488 Patented June 21, 1960 portant in the attainment of the desired high speed and therefore a zinc bronze alloy is preferred for the production of the insert. However, certain ofthe advantag'es of the invention may be obtained through the use of inserts formed of other metals. For example, other bronze alloys, such as a lead-bronze, may be used, this having good compatibility with the metal of the rib but being somewhat softer and less wear resistant than the zinc-bronze alloy. Still other metals having comparable compatability, hardness and wear resistance may be substituted for thezinc bronze alloy in the production of the insert.

This has resulted in exceshook shaft outwardly through the center of curvature of the raceway. The maximum bearing pressures are created in that region with the result that the bearingsurfaces of the raceway becomes worn and roughened and fine particles of metal are frequently formed which become incorporated in the lubricant and tend to soil the thread and the work.

By the present invention it has become possible to increase the speed of a rotary hook to 13,000 r.p.m. which permits the formation of stitches at the rate of 6500 per minute. This has been achieved by providing a special insert in the hook body in the region of maximum eccentricity of the raceway. The insert is formed of a metal having such compatibility with that of the cooperating rib on the bobbin case holder as to greatly reduce the welding, seizing or galling tendency of the rubbing surfaces. The rib specified is =formed of hardened steeland is preferably chromium plated. It has been found that a highly satisfactory metal for the production of'the insert mentioned is a zinc-bronze alloy. This has good Wearing qualities, sufficient hardness to resist deformation under the forces applied in the high speed revolution of the hook and has excellent compatibility, i.e. minimal tendency to produce welding, seizing or galling, with the hardened steel rib, especially when the latter is chromium plated. All of -the' characteristics mentioned are;.im-.'

The insert of the present invention should extend over a suitable arcuate portion of the raceway in the indicated region. It should extend over an arc of at least 45 and preferably about 60, and it may extend over a greater are. However, certain considerations should be observed in the location and arcuate extent of the insert. Thus in its application to a hook of the character disclosed in the patent to Covert et al. No. 2,694,373, granted November 15, 1954, the raceway in the hook body and the rib on the bobbin case holder are both discontinuous. The raceway has a section which extends from a point adjacent the base of the hook beak rearwardly through an arc of' about 170. In this construction the point of maximum eccentricity of the raceway is about 143 in rear of the hook point'and the insert should extend forwardly from the rearward end of the 170 are mentioned. It should terminate at least a short distance rearwardly of the base of the hook beak, since if it extended throughout the 170 arc the pounding of the forward end of the insert, which would, then define the leading or forward end of the raceway section mentioned, against one of the free ends of the discontinuous rib on the bobbin case holder would soon become distorted and destroy the smooth entrance to the raceway. Beyond the 170 section mentioned the raceway continues for about. another but the wall of the hook body in this region is thinner and the top or outer wall of the raceway is provided by an angle member secured to the hook body. There would be no serious objection to extending the insert into this region but it is unnecessary to do so and would involve complications.

Other important features of the invention will appear from thedetailed description of an illustrative embodiment of the same whichwill now be given in conjunction with the accompanying drawings, in which:

Fig. 1 is a plan view showing the improved rotary hook mounted on the hook shaft in the base of a lookstitch sewing machine and showing also a cooperating member having a finger for preventing rotation of the bobbin case holder;

Fig. 2 is a side elevational view of the rotating hook body of the rotary hook unit;

Fig. 3 is a face view of the hook body;

Fig. 4 is an axial sectional view through the hook body taken along the line 4-4 of Fig. 3;

Fig. Sis aperspective view of a member secured to the hook body and serving as a gib providing one wall of a section of the raceway and serving also as a thread retainer;

Fig. 6 is a plan view of a bobbin case holder carried by the hook body; p Fig. 7 is an axial sectionalview through the hook bodytaken along the line 7-7 of Fig. 3; p 1

Fig. 8 is a perspective view of the hook body with certain attachments removed;

Fig. 9 is a perspective view of the hook body taken from'a diiferent angle and showing the gib of Fig. 5 and a thread guard secured thereto; a :Fig. 10. isaperspectiVe'VieW, of-the thread guard cal- 3 ried by the hook body in a region extending circumferentially from the hook beak to the region of the rearward end of the special insert;

Fig, 11 is a plan view of the insert;

Fig. 12 is. an elyational view of the. inner face of. the

n er Fig. 13 is a sectional view, through. the insert taken along the line 1313 of Fig. 12; and

Fig. 14 is an enlarged elevational view of the insert as seen from the right in Fig. 12. i

The improved rotary hook may be applied to lockstitch sewing machines of a variety of diiferent constriuc: ign Typi a e k itchmachines to which. the invert.- p m y b pp ie a h ni'n the pa nts t h ms' sen et al. No. 2,113,572 granted April 12, 1938; Reimer, No 2,643,625granted June 30, 1953; andI-Iale et. al. No. 2,752,325 granted September 11,1956.

' Referring" now to the drawings, the machine is. provided with a rotary hook shaft (Fig. l) in the base of the machine adapted. to be driven at double the anlar speed of the main drive shaft. of the machine. By virtue of the improvements of the present invention it is possible to rotate the shaft 10 at 13,000 rpm. without excessive wear and other difiiculties encountered with rotary hooks as previously constructed when operated at speeds higher than about 10,000 rpm. The rotary hook has a main bodyll having a hub portion 12 by which thehook body 'mayfbesecured to the shaftltlbymeans ofsetscrews 131 The hook body has atop-shaped portionprovidingthecavity 14 for the reception; of abobbin caseholder 15 of the character-shown in Fig. This bobbin case holder has a circumferentially extending rib 16 which isinterrupted 'in theregion indicated at 17 to enable the/passage of -the needle thread loop around the-same and-to enable the-release-of the loop at the appropriate time in the cycle of stitch formation. This interruption in the rib is in a region adjacent the top of thevbobbin case and opposite a notch 18- in its outer facewhich cooperates with-a detaining finger 19 (Fig.- 1) carried bya plate 20 secured to the. under-surfaceofthe usualcloth plate of the machine. It will beunderstood that'the finger 19 prevents rotation'of thebobbin case holder.by. -the frictional drag of the rotating hook body. Thebobbincase-holder is prefe'rably. formed of hardened steel and'the rib 16 is preferably, though not necessarily, plated with a relatively: hard chromium-finish. Such'a plating. has good wear resistanceand an exceptionally good compatibility with various bronze's-and 'other metals of which the special insert for theraceway isformed;

The rib 16-on the bobbin case holder cooperate s with a raceway extending. circumferentially of*the--wall ofthe hook body which defines the cavity 14. This raceway isv in part cut or otherwise formed directly in saidwall of the body andis in part closed at its outer'side by means of'a gib and thread retainerZl (Fig. 5) whichis secured by screws 22 to the wall ofthe hookbody; Member 21 has an inwardly extending-flange 23 which forms the outer wall of the'raceway inthe hook body, as best shown in Fig, 7; It, will beund'erstood that the peripheralj surface: of therib,16; cooperates. with the inwardly facing surface, 24 of the-hook raceway formed in the hookbody andthe bobbin case holder is held against any appreciableaxialrmovement in relation to the-hook body by the fiange, 23. and by, a corresponding, opposed inwardly extending wall 24a, Fig. 7, on the portionof the raceway cut or otherwiseformedcompletely within the hook body itself. 7 AS, indicated;hereinbefore, the peripheral wall 2410f the raceway is slightly eccentricgtoztheaxisot :thedriping 10. Thiseccentricity, whichmay: suitably be about .0015 of an inch to accomplisht-he; intendedzpurpose. may be provided in-;anyof a;-num ber of-different w ay's. One simple wayis to;fi1 1 i$h a borea 25 through-the hub 12. of the hook body after-the racewayhas been;.-finished At t is tinge-it is. elatire r-ssimpleetcprovideaha desir d eccentricity of. the bore 25 in relation to the center of curvature of the raceway in the desired direction.

Referring to Fig. 3, the relationship of these various surfaces is indicated, the extent of the eccentricity being exaggerated. The axis of the bore 25, and hence of the shaft 10, is indicated at- 26- while the center of curvature of the hook raceway is indicated at 27. The spacing betweenthesepoints indicated, on an exaggerated scale, by the distance EE- between the two radial lines shown, In the preferred construction the distance hetweenthe two centers is only between- .001- and .002 of an inch. This is sufiicient to set up the forces necessary to open up a gap at the proper time between the shoulders which prevent rotation of the bobbin case holder. The direction of maximum. eccentricity; ize. of the center of curvature of the raceway in relation to the axis of the hook shaft, is along the line 77 and in the downward direction. along-that. line. This places the point ofmaximum eccentricity of: the raceway at-a suitable. angle, preferably. about. L40", rearwardly of the tip 2-8, of the hook-.-b.cak which seizestlie needle thread loop in operation. offthc-hookv Irn-this region of the hook body the circumferential wall.'2j9., defining the. cavity 14, is cut away Quits-inner face toprovide a relatively thinwall 3.0 and tow form arecess in which is fitted an insert 31 of the character above. discussed. The. cutting. away of the wall. 29' to provide, the recess for they insert is done whilethe hook body is in an unhardened state. The hook. body is then subjected to. the necessary heat. treatment for hardening and theinsert 31 is thenintroduced and secured to the wall 30, pre'ferabaly by the use of a relatively low melting solder. The insert may, however, be secured in place by screws or rivets or by any other suitable means. When the parts are assembled the hook body is subjected to a final finish grinding operation which insures the desired smooth surface throughout the raceway and the properrnerging of that portion of the raceway supplied by the insert 31 withthe other portions thereof. I

Rcferringinow to Figs. 11-14, the preferred form of the insert 31 is, indicated. It will be notedthat the insert ha'sa wal1j 3 1'a which extends to the top of the wall 2311f "the hookhod'y. At an intermediate point the wall 31a of the insertsomewhat thicker and extends in.-

wardlyto a slight extent to provide a smooth, arcuate 'sur fa'ce l'r l b against which the rib 161011 the bobbin case holder bears. Surface 31b,.therefore, forms a part of the nook-raceway; There is no overhanging shoulder, however, which closesthe; outer end of the raceway in this-regiom At thejbottom of the insert there is a stillfurther inwardly, projectingportion. 310 which pro.- videsabottomwall for the hook raceway in the region of-"th'e insert. The inner face of the rib 16 rests upon orc'ooperateswiththe topsurface of the projection 31c. Atit'send farthest removed from'the' hook beak 28 the insert is provided with a sloping surface 31d. Secured to the circumfejrential face of the'hook body is a thread guard 32' (Figs. 9 and 10)"this being secured to the hook body by -screws- 33 Thread guard 32 at its rearward end, positioned inthe region of thesloping-surface 31d on the'in'sert; has an outwardlyprojectingportion 32a cpposit'ea'the surfacefilil'd. A notch 32b provided; in the rearward end of theguard 32 enables the passage-of the-needle downwardly intocooperation-withthe hook at the:a propriat time'in thecycle of revolution of thehook body-. -A-"surface 32c; which partially defines the notch; 32b is:s1oped to conform=substantially with the v slope of surface 31 d on the insert; At its forward end the-thread -guard extends to a position adjacent --the hook be'akand cooperates: with the latter inretainingthe seized loopof needl'ee thread iii-proper relation to the rotatinghook-body. V

Thehookbody has integral inwardly extending flange- 34 providing an outer wall for -a; portion of the hookraceway. This fiange-extends'froma point-adsv t iacent the beak 23 of thehook to a point adjacent the forward end of the insert 31. As has been explained, another portion of the hook raceway is closed at its outer side by the flange 23 of the gib member 21. This closedin portion of the raceway extends from the rearward end of the insert substantially to the threadretaining point 35 of the gib 21. This point extends into a region adjacent the hook beak 28 and the forward end of the thread guard 32. u

As has been indicated, it is of primary importance that the insert 31 extend over an arc of say 45 or more in the region of maximum eccentricity of the hook raceway, i.e., adjacent the lower end of the line 7-7 in Fig. 3. It is at this point or in that region that the maximum pressures are created on the raceway and hence the greatest tendency toward wear, seizing, welding and galling takes place. The insert should extend over an arc of at least about 20 on each side of the point of maximum eccentricity of the hook raceway and it may, if desired, be extended forwardly a greater distance toward the hook beak 28. However, an insert extending over an arc of more than about 60 adds little, if any, advantage to the construction. Furthermore, it is essential that the leading or forward end of the hook raceway in the region of the hook beak be formed of hardened steel or the like since the softer and less wear resistant material of which the insert is formed would not withstand the pounding to which this forward end of the raceway is subjected as it approaches and sometimes strikes against the end of the rib 16 at one side of the interruption 17 therein.

As has been indicated, the insert 31 may be formed of any metal having the requisite combination of properties such as good wear resistance, adequate hardness to resist deformation under the pressures created in the region of maximum eccentricity of the hook body and good compatibility with the cooperating metal of the rib on the bobbin case holder. A metal which has been found especially satisfactory is a zinc-bronze sold by the Mueller Brass Company under the designation 600. The composition of this 600 alloy is approximately as follows: copper, 58%; manganese, 2.5%; silicon, 0.75%; aluminum, 1.5%; and the balance zinc. This alloy has been found to have a compression yield strength at .2% offset of 73,000 lbs. per square inch. Rods extruded from the alloy have been found to have a Rockwell hardness (B scale) of 75 while rods cold drawn from the alloy have been found to have a Rockwell hardness (B scale) of 80-84. It has very good compatibility with hardened steel and especially so with chromium plated hardened steel.

The.Mueller Brass Company has a number of zincbronzes in what it calls the 600 Series. The No. 600

discussed above has been found most satisfactory for the purpose of the present invention. However, other members of the 600 Series (I.E., 601, 602, 603, 604 and 605) are quite satisfactory for the production of the "insert. All of these bronzes contain approximately 60% copper and at least 34% zinc. Only the type 600 contains aluminum, but the 602-605 types contain small percentages (i.e., .5 to 2.5%) of lead. Other leadbronzes may be used for the purpose of the invention but, as indicated above, they do not have as high wear resistance as the zinc-bronze mentioned and they are somewhat softer and therefore cannot withstand as high bearing pressures as the zinc-bronzes mentioned. On the other hand, the lead-bronzes have some advantage in the respect that they do not have quite as great a tendency' to heat up as the zinc-bronzes. Other alloys having the requisite properties enumerated above may also be used for the production of the insert.

While a preferred form of the invention has been disclosed in considerable detail and certain modifications have been suggested, it will be understood that other variations and modifications may be made within the I principles and the scope of the invention.

What is claimed is: I

1. A rotary hook for a lockstitch sewing machine which comprises a hook body provided with a 'hub for mounting said body on a rotary shaft of said machine, said hook body havinga cavity provided with a raceway in thewall thereof, a bobbin case holder positioned with in said cavity and having a radially extending rib having its peripheral surface in bearing engagement with the circumferential wall "of said raceway, said body having a loop seizing beak thereon, the raceway in said body being eccentric to the axis of said hub, the center of curvature of said raceway being along a radial line extending from the axis of said hub at such a predetermined angle to a radial line from said axis to the tip of said beak as to provide a hook opening action, said hook body and said bobbin case holder being formed of hardened steel, and a metal insert fixed in said body and extending circumferentially thereof to provide a smooth continuation of the surface forming the circumferential wall of the raceway in a region of said raceway extending in opposite directions from said first-mentioned radial line, said insert being formed of a metal different from and compatible with the hardened steel rib of said bobbin case whereby the welding and gallin-g tendency of said raceway in relation to said rib during high speed relative movement is greatly reduced.

2. A rotary hook of the character set forth in claim 1 in which said insert is formed of zinc-bronze;

3. A rotary hook of the character set forth in claim 1 in which said insert is formed of a relatively hard, wear resistant bronze.

4. A rotary hook of the character set forth in claim 1 in which said insert extends over an arc of at least 45 5. A rotary book of the character set forth in claim 1 in which said insert extends over an arc of between 45 and 6. In 'a lockstitch sewing machine a horizontally disposed rotary shaft, a rotary hook body secured to said shaft, said hook body having a cavity therein forming a cup-shaped portion surrounding the axis of said shaft, said portion being provided with a raceway in the axially extending wall thereof, a loop seizing beak extending from said wall, said raceway being eccentric to the axis of said shaft, the center of curvature of said raceway being along a line extending radially from the axis of said shaft in such a predetermined angular relation to a line extending from said axis to said loop seizing beak as to provide a hook opening action, a bobbin case holder formed of hardened steel and disposed within said cavity, said bobbin case holder having a radially extending rib having its peripheral surface in bearing engagement with the circumferential wall of said raceway in the hook body, means for restraining rotation of said bobbin case holder with said hook body, means fixed in said hook body providing a smooth continuation of the circumferential wall of a portion of the raceway therein in the region intersected by said first-mentioned line, said last-mentioned means being formed of a metal which is relatively hard and wear resistant and is different from and compatible with the cooperating metal of said rib, whereby welding, seizing and galling tendencies of the cooperating surfaces of said rib and last-mentioned means are relatively low at high speeds of rotation of said hook body.

7. In a lockstitch sewing machine of the character set forth in claim 6, said last-mentioned means being formed of a bronze alloy.

8. In a lockstitch sewing machine of the character set forth in claim 6, said last-mentioned means extending over an arc of at least 45 and having at least a 20 arc on each side of said first-mentioned line.

9. In a lockstitch sewing machine of the character 'set' fbrth in claim 8, said insert extending over 'a n ar'c of between 45 andl 'lll j 10, In a loekstitch sewing machine bf the Character set in claim 6, said rib on said bobbincase holder being chrqmium plated. I

, 11,5111 5160mm. sewing machine. of the character setv forth in elaim.6,e the 'end 9f saidlast-mentionedmeans adjacentsaidlloop. seizing beak terminating some distance readwardly 'ef said beak, said beak and the. adjacent portion of said raceway being fenned ofhairdened" steel.

Referenees Cited in the file of this patent UNITED STATES EATENTS 1,049,791 Winkel Jan, 7;. 19 1 3? 5 "1,351,869; 'Petti Sept.'l7, 1920.-

2;s23,230: Petskeyes Sept. 1 9; 195'0'. OTI-I -ER' REFERENCES" Metallurgy ofthe Non Ferrous Metals? (Dennis); .r published by. Pitman & Sons, Ltd. (London); 1954, (pages'163; 164 and'389relie 1en); I 

